Influence of asymmetric inflow on the transient pressure fluctuation characteristics of a vertical mixed-flow pump

Abstract

In order to investigate the influence of asymmetric inflow on the internal flow fields of a vertical mixed-flow pump, numerical simulation of unsteady flow was carried out under four inflow angles ( θ = 0°, 10°, 20°, and 30°). The reliability of the calculation results was validated through an external characteristic experiment. The fluctuation value of the pressure was defined to obtain the transient pressure fluctuation intensity distribution. Three monitoring points were arranged to compare pressure fluctuation characteristics under different inflow angles. The results suggested that the increase in the inflow angle caused the design operation points to deviate to the over-load flow rate. When the inflow angle increased from 0° to 30°, the axial velocity distribution coefficient and weighted average angle at the inflow runner outlet both decreased. The overall transient pressure fluctuation intensity inside the impeller increased, especially on the pressure side of the blade. Additionally, the transient pressure fluctuation intensity on the pressure side of the guide vane also increased significantly. As a result, the amplitude of pressure fluctuation at the dominant frequency of each monitoring point increased. Relatively speaking, the negative influence of asymmetric inflow on the operational stability of the pumping station was further extended under the part-load flow rate.